Numerical Analysis Of Seismic Performance Of Seismically Damaged Reinforced Concrete Columns Reinforced By Enlarged Section Method

Reinforced concrete(RC)structures can experience varying degrees of damage or even collapse when subjected to seismic loads.However,if the structure does not completely collapse and demolition and rebuilding are not feasible,seismic rehabilitation and strengthening become necessary.This can improve the seismic performance of the structure,meet subsequent use function requirements,and reduce economic losses resulting from earthquake disasters.In reinforcement engineering,the increased section method is an economical and reliable direct reinforcement technique that effectively enhances the strength,stiffness,ductility,and seismic performance of concrete structures,and is therefore widely employed.Accordingly,this study selects the increased section method to strengthen seismic damaged RC columns.In this thesis,a numerical model for seismic damaged reinforced concrete(RC)columns was established using ABAQUS finite element software.Subsequently,a numerical analysis model for seismic damaged reinforced columns was developed and the accuracy of the numerical models of RC columns under different degrees of seismic damage was compared and analyzed.Additionally,the seismic performance of RC reinforced columns was compared and analyzed with and without considering seismic damage to investigate the differences in reinforcement effects between different reinforcement methods.Finally,the seismic performance of reinforced columns with or without consideration of seismic damage under different axial pressure ratios was also analyzed,leading to several significant conclusions.(1)The seismic damage characterization method,which integrates the structural skeleton curve characteristic points and displacement angles,can be employed in ABAQUS numerical analysis software to more precisely simulate various degrees of seismic damage of a column,given that the fundamental parameters of the column are known.The relative errors between the numerical calculation results and test results are below 30%,indicating that the numerical analysis model of the seismic damage RC column is reasonably accurate.(2)Seismic damage significantly impacts the seismic performance of reinforced columns.Under identical displacement conditions,the energy dissipation capacity of strengthened columns considering seismic damage was found to decrease by over 33% compared to those without seismic damage,while the ductility increased by up to 17%.However,the initial stiffness of the reinforced column cannot be fully restored,and heavily seismically damaged reinforced columns with increased axial compression ratio exhibit reduced ductility.These findings suggest that the ductility of reinforced columns may decrease if seismic damage is not taken into account.In practical strengthening projects,the prerequisite conditions of seismic damage should be comprehensively considered to achieve better strengthening effects.(3)Strengthening seismically damaged concrete structures using the increased section method can lead to a significant improvement in their seismic performance.Numerical simulations of moderate seismic-damaged reinforced concrete(RC)columns reveal that the increased section method results in better strengthening effects,with a 37% increase in energy dissipation capacity and a 28% increase in initial stiffness.These findings suggest that the increased section method is an effective means of enhancing the seismic performance of concrete structures.(4)The seismic performance of reinforced columns that have been damaged by earthquakes is significantly affected by the axial pressure ratio.Various calculations conducted at different axial pressure ratios have revealed that the energy dissipation,stiffness,and ductility of the strengthened columns decrease as the axial pressure ratio increases from 0.6 to 0.9.Specifically,the energy dissipation,stiffness,and ductility decreased by 29%,42%,and 11%,respectively.The reinforcement of the seismic-damaged column was carried out under holding load,and the trend of stiffness change of this reinforced column was significantly different from the stiffness change of the unholding reinforced column.Therefore,in actual strengthening projects,it is essential to comprehensively consider and limit the effect of axial compression ratio.The present study demonstrates that seismic damage can be characterized by the characteristic points of the skeleton curve obtained from column loading and the corresponding displacements,given that the fundamental parameters of the column are known.In practical strengthening projects,it is crucial to consider the effects of seismic damage and axial pressure ratio on the strengthened column before initiating the strengthening process.This will enable an accurate analysis of the impact of the strengthened column.